Ultrasonic beam scanning technique and apparatus

ABSTRACT

A beam of ultrasonic energy emitted from a stationary transducer is scanned through the use of a steerable mirror which is positioned in the path of the beam between the transducer and a target. The mounting means for the steerable mirror enables the beam of ultrasonic energy to be aimed as desired and the beam will preferably be scanned along a line and the scanning line may be shifted in a generally transverse direction to accomplish &#34;Multiple plane&#34; scanning.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to non-destructive testing andparticularly to the non-invasive examination of soft tissue and bodyorgans. More specifically, this invention is directed to medicalultrasonic equipment and particularly to pulse-echo body scanners.Accordingly, the general objects of the present invention are to providenovel and improved methods and apparatus of such character.

(2) Description of the Prior Art

While not limited thereto in its utility, the present invention isparticularly well suited for use in diagnostic medicine. Apparatus andtechniques which permit the non-invasive examination of soft tissueorgans are, for obvious reasons, of considerable interest. Presentlyavailable techniques for performing "imaging" of soft tissue organsinclude x-ray, nuclear medicine, thermography and, to a much lesserextent, diagnostic ultrasound. Nuclear medicine is, of course, aninvasive technique, thermography has very limited utility and the degreeof information which can be provided by conventional x-rays is limited;i.e., x-rays are not well suited for the imaging of soft tissues.Further, with imaging techniques other than diagnostic ultrasound, theremay be some restriction to repeating the test if inconclusive resultsare obtained. In the case of nuclear medicine, for example, aninconclusive or unsatisfactory radioisotope scan may require the patientto be subjected to the reinjection of the radioisotope. As an additionaldisadvantage thereto, radioisotope scans and x-rays are notoriouslyexpensive procedures.

Ultrasonic diagnostic techniques, because of the very high benefit torisk ratios for the patient and the ability to perform imaging of softtissue organs that no other modality can provide, are attracting everincreasing interest. Thus, ultrasonic diagnosis has found applicabilityin obstetrics and gynecology, cardiology, neurology, ophthalmology andurology in addition to crossing over medical disciplines with theimaging of various internal body organs. In some situations invasivetechniques for studying the heart, such as cardiac catheterization andangiography, can be replaced by ultrasonic techniques. Similarly,ultrasonic diagnosis has found use in the diagnosis of mitral stenosis.The widespread utility notwithstanding, the adoption of this modalityhas been impeded by inherent limitations in the equipment previouslyavailable.

Ultrasonic diagnostic instruments operate on either a pulse-echo orDoppler principle. The pulse-echo principle, which is primarily used forthe imaging of soft body tissue, involves the transmitting of shortbursts of ultrasonic energy and recording echoes reflected from anatomicstructures within the body. Since the time required for an emitted pulseto return as an echo indicates the distance of the target structure fromthe transducer, the "echo gram" provides both a picture of the objectand a graphic recording of any changes in the objects position. Thus,ultrasonic diagnosis is based on the reflection of ultrasonic waveswhich occur at the boundaries between different tissues within the body.A fraction of the incident energy is reflected if there is a change incharacteristic impedance at such a boundary; impedance being defined asthe product of the density of the tissue multiplied by the velocity ofsound. Although the echoes which correspond to soft tissue boundarieshave very small amplitudes, these echoes can be detected by a receiverhaving the requisite sensitivity. Energy which is not reflected travelsbeyond the boundary, and may be reflected at deeper boundaries. Themaximum penetration is limited by the attenuation of the ultrasonic wavein passing through the tissues; attenuation being defined as thedecrease in intensity of the sound pulse per unit of distance as itpropagates in the medium and loses energy as the result of absorptionand scattering.

Ultrasonic diagnostic instruments employ a transducer which convertselectrical signals into acoustic pulses which are coupled into thetissue of the patient. The transducer may also serve the dual functionof receiver for detecting the reflected pulses from within the patient.The transducers employed in ultrasonic body scanners are typicallypiezoelectric elements comprised of ceramic materials such as syntheticlead zirconate titanate. An ultrasonic diagnostic instrument will alsocomprise an oscillator which establishes the pulse repetition frequencyand a linear power amplifier which excites the transducer through acoupling circuit. A decoupler permits the transducer to be used as botha transmitter and a receiver. The received pulses; i.e., the echoesreturned from within the patient's body; are converted into electricalsignals in the manner known in the art, these electrical signals areprocessed and the processed signals are presented on a display. Thedisplay will typically be a cathode ray tube and the oscillator whichcontrols the transducer may also be employed to generate a time basetrace for the display.

In order to obtain maximum utility from the instrument, two-dimensionalimages of various organs or body regions of interest must be generated.This can be accomplished by "scanning " wherein the transducer is movedback and forth. In the prior art the most common method of scanninginvolves contact scanning in which the transducer is placed directly onthe patient's skin and moved, through a type of compound scan, instepwise fashion. The information obtained must be optimized throughcoordinated movement of the transducer to achieve a meaningful image.Accordingly, a high degree of skillful operator interaction with theinstrument is essential for a successful ultrasonic examinationemploying prior art equipment and it has been exceedingly difficult toduplicate initial test results since repeatability was almost totallydependent upon operator placement of the transducer.

The high degree of operator skill required and the extreme difficulty inrepeating test results have, in part, been a consequence of the use ofsmall size contact transducers; this small size resulting from thenecessity of fitting the transducer to the contour of the skin. Priorart ultrasonic body scanners, as a consequence of their use of smallcontact transducers, were also characterized by slowness of use sincethe ability to find the area of interest was limited to trial and errorscans. It is to be noted that the small size of the transducers, theslowness of the procedure and the difficulty in obtaining repeatabilitywas also attributable to the fact that the prior transducers andassociated apparatus lacked both the ability to electronically focus the"beam" of ultrasonic energy over the entire examination depth ofinterest and the ability to easily aim the "beam".

Prior ultrasonic diagnostic equipment has also been characterized byinsufficient resolution over the desired examination range in the body;this examination range or field of examination typically being on theorder of 20 centimeters. In order to be practical, an ultrasonicdiagnostic device must have the ability of providing real time images ofhigh resolution. The required characteristics, which result only fromminimizing beam width and side lobes, have been lacking in the priorart. A further deficiency of prior art ultrasonic body scanners hasresided in their poor dynamic range. The returns or echoes from thesignal propagated into the body may vary over a range of 100 db. It isimpossible to record the 10⁶ shades of gray which correspond to a 100 dbrange. It is, accordingly, prior practice to compress the signalsgenerated by echoes through either the use of logarithmic amplifiers orby simple time gain compensation circuits. Using the prior artcompression techniques, however, important information contained in thereceived signals has been lost.

With particular respect to the transducers employed in the prior art, asbriefly noted above the transducers previously used have not beencapable of being focused electronically to achieve variable examinationdepth. Prior art transducers have typically been of a flat contour;i.e., have had no natural focus; and accordingly have been characterizedby large magnitude side lobes which give spurious signals from off-axistargets and also result in ambiguity in range measurements because ofthe different path lengths for the echoes from the same object.

SUMMARY OF THE INVENTION

The present invention overcomes the above briefly discussed and otherdeficiencies and disadvantages of the prior art and in so doing providesa novel technique and apparatus for causing the scanning of a focusedbeam of ultrasonic energy. The invention comtemplates use of a steerablemirror positioned between the transducer which produces the beam ofultrasonic energy and the surface of the body being subjected to anon-destructive testing procedure. In a preferred embodiment the mirroris a flat plate and the ultrasonic energy is coupled to the mirror andthence to the test object via a liquid path.

In the disclosed embodiment, the mirror is supported in such a mannerthat it may be aimed in any direction. The support means includes aflexible member which also functions as a seal to prevent leakage of theliquid which defines the path for the ultrasonic energy between thetransducer and a test object. The support means also includes a bearingmember affixed to the back of the mirror and having a bearing surfacewhich is in the form of a portion of a sphere. A drive shaft extendsfrom the bearing member and is engaged by a first end of a pivot arm towhich a rocking motion is imparted whereby the mirror is tilted in sucha manner as to cause the ultrasonic beam to scan along a line. In thepreferred embodiment means are also provided to generally transverselyshift the line of scanning by effectively changing the length of thepivot arm. The scanning along a line will typically encompass stepwisemotion and the shifting of the line will also preferably be in steps toaccomplish multiple plane scanning.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood and its numerous objectsand advantages will become apparent to those skilled in the art byreference to the accompanying drawing wherein like reference numeralsrefer to like elements in the various figures and in which:

FIG. 1 is a perspective view of a first embodiment of an ultrasonic bodyscanner in accordance with the present invention;

FIGS. 2A and 2B are respectively front plan and cross-sectional sideelevation views of a first embodiment of a transducer crystal which maybe employed in the apparatus of FIG. 1;

FIG. 3 is a rear plan view of a second embodiment of a transducercrystal which may be employed in the apparatus of FIG. 1;

FIGS. 4A and 4B are respectively front and rear plan views of a furtherembodiment of a transducer crystal which may be employed in theapparatus of FIG. 1;

FIG. 5 is a cross-sectional side elevation view of the transducer headof the apparatus of FIG. 1;

FIGS. 6 and 7 are respectively top and cross-sectional side elevationviews of the beam scanning control mechanism of the apparatus of FIG. 1,FIG. 7 being a view taken along line 7--7 of FIG. 6;

FIGS. 8A-8C inclusive comprise a functional block diagram of anelectrical control circuit for the apparatus of FIG. 1;

FIG. 9 is a schematic illustration of the electrical focusing of anultrasonic transducer in accordance with the present invention; and

FIG. 10 is a wave form diagram related to the control circuitry of FIG.8.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference now to FIG. 1, an ultrasonic body scanner in accordancewith a first embodiment of the present invention is shown. The bodyscanner includes a head assembly, indicated generally at 10, whichhouses a transducer and means for controlling the scanning of the beamgenerated by the transducer. The present invention employs a transducerwhich preferably has a comparatively large area. Also, the transducersemployed in the present invention are preferably also characterized byhaving a natural focal length. Since a large area transducer will notnormally conform to the contour of the patient's body, flexible meansmust be provided to couple the ultrasonic energy from the transducerinto the patient. In the disclosed embodiment the coupling meanscomprises a flexible bladder 12 filled with a liquid such as waterand/or other liquid with low sound absorption qualities. As will be seenfrom FIG. 5, the front face of the actual transducer element is immersedin the fluid within bladder 12. This offers the important advantage ofpermitting high speed sector scanning without repositioning the headwith respect to the patient. Also, separation of the transducer from thebody permits focusing of the beam of ultrasonic energy close to thepatient's skin line.

Head 10 is supported on the free end of an articulated arm which hasbeen indicated generally at 14. The construction of arm 14 is such thathead 10 may be raised, lowered, moved toward or away from the supportcolumn 16 for arm 14 and pivoted about the axis of the support column16. Thus, head 10 has six degrees of freedom of motion whereby any planein the body can be visualized and objects such as veins can be trackedas they course through the body. Head 10 is mounted from arm 14 via apair of yokes 22, 24 which permit a limited degree of movement of thehead with respect to the arm so as to permit optimizing the contactbetween bladder 12 and the patient. A control panel 18 is also mountedon arm 14 immediately above head 10. Through use of controls on panel 18the operator may select the scanning mode of the transducer within head10 and particularly the rate, area and depth of the scan. The operatormay also, via control panel 18, control the taking of photographs ofregions of interest. The movements of head 10 are physically controlledby the operator; i.e., the position of the scanning head on the patientis manually changed by steering the head through use of a pair ofhandles 20, 20'.

A monitor 26, which may be a conventional television receiver, ismounted from the support column for the arm mechanism 14 as shown. Themonitor 26 is positioned so as to provide the operator with a visualpresentation of the area being scanned whereby the operator will beassured that the head is properly positioned and will be giveninformation which will enable him to change scanning modes, for examplefrom a fast to a slow scan, and to activate the camera.

The power supplies and control circuitry necessary for operation of thebody scanner, as well as the circuitry for processing received signals,are mounted in a pair of equipment cabinets 28 and 30. Cabinet 30includes, in addition to a main control panel, an "A" scan scope whichis typically a cathode ray tube. Scan scope 32 displays the raw signalproduced by the transducer in head 10 in response to the receipt ofechoes; i.e., the scope 32 displays echo amplitude versus time (depth).The "A" scan provides information to the operator which is initiallyemployed for adjusting the gain controls of the apparatus so as toachieve equal amplitude for signals commensurate with echoes receivedover the entire range of depth of examination. The "A" scan alsoprovides information, not easily ascertainable from photographs, as tothe magnitude of the received echoes. This information may be ofinterest in interpreting the results of an examination. In response tothe information provided on scope 32, typically at the beginning of anexamination, the operator will adjust a time gain control which isactually a curve shaping control. Equipment cabinet 30 includes afurther cathode ray tube and a TV camera tube which are employed toproduce and transmit a two-dimensional image back to the TV monitor 26.The signal displayed on the cathode ray tube in cabinet 30 will be theraw signal from the transducer processed so as to give a two-dimensionalbody scan. A camera 34 is mounted on cabinet 30 so as to permit themaking of a permanent record of the results of the scan; camera 34taking a picture of the display on the cathode ray tube and beingcontrolled from panel 18 as discussed above.

Referring now to FIGS. 2-4, various transducers which may be employed inthe practice of the present invention are depicted. The transducers arefabricated from a wafer or disc of piezoelectric material, typically aceramic such as lead zirconate titanate, and preferably have the commoncharacteristic of a concave front or emitting surface and a convex rearsurface as may be seen from FIG. 2B. The transducer could, however, be aflat crystal having a concave acoustical lens bonded to the frontsurface thereof. In such case the lens would typically be fabricatedfrom a plastic including a suitable filler which gives the desiredpropagation velocity. The lens material should also have an absorptioncoefficient of zero, an impedance which is matched to that of thecrystal and a refractive index which is not unity. Thus, the transducersemployed in the preferred embodiment of the invention have a naturalfocus which will typically be 30 centimeters from the center of thetransducer. In order to permit energization of the transducers by theapplication of an electrical signal, to thereby generate a sound pulse,all or portions of the opposed faces of the ceramic wafer must be coatedwith electrically conductive material. The presence of such electrodeson the transducer also permits the sensing of electrical signalsgenerated by the piezoelectric material in response to pressures appliedto the material commensurate with received echoes.

FIG. 2 depicts a transducer electrode configuration particularly wellsuited for the imaging of tumors. In the FIG. 2 embodiment the entirefront surface of the tuned piezoelectric wafer 40 is coated with a layerof conductive material 42 as may be seen from FIG. 2B. As best seen fromFIG. 2A, the opposite or back surface of wafer 40 is, with the exceptionof a pair of annular regions, also completely coated with the electrodematerial as indicated at 43. These two annular regions define, in theircenters, a pair of discrete electrodes 44 and 46. Electrode 44 isdisposed on the axis of the transducer while electrode 46 is displacedfrom the axis. The discrete electrodes 44 and 46 are employed only inthe receiving mode.

FIG. 3 depicts, in a plan view, an electrode configuration which may beemployed for both the front and back surfaces of the shapedpiezoelectric wafer. The electrode of FIG. 3 is characterized, extendingoutwardly from the axis thereof, by a plurality of concentric rings 49of electrode material; the circles of conductive material being alignedon the opposed faces of the transducer. Use of a plurality of concentriccircles of electrode material on at least the back surface of thepiezoelectric wafer permits the electronic focusing of the transducerwhereby the examination depth may be varied about the natural focallength of the transducer. Also in accordance with the FIG. 3 embodiment,the outer electrode ring 47 is segmented. The segmented electrode isemployed for receiving purposes only. It has been found that, to obtainoptimum results, the width of ring 47 should be less than tenwavelengths of the transmitted ultrasonic energy and should preferablybe about three wavelengths.

As an alternative to the electrode arrangement depicted in FIG. 3, it ispossible to employ an annular lead zirconate titanate crystal, having awidth which corresponds to one-half the wavelength of the transmittedultrasonic signal, on which the segmented electrodes are deposited. Aseparate transmitting transducer would, in this case, be mounted on theaxis of such an annular transducer.

Considering FIG. 4, a further embodiment of a transducer for use inaccordance with the present invention is depicted. In the FIG. 4embodiment, as shown in FIG. 4A, the entire front surface of the tunedor focused piezoelectric wafer is covered with electrode material. Therear surface of the transducer, as may be seen from FIG. 4B, isidentical to the electrode configuration of FIG. 3 with the exceptionthat the segmented outer electrode is omitted. The focal length of thetransducer of FIG. 4 may be varied electronically about the naturalfocal length.

The discrete electrodes of the FIG. 2 embodiment may be incorporatedinto any of the other disclosed transducer embodiments.

To discuss further the above described transducer configurations, inpulsed ultrasonic body scanning, and particularly in B-mode scanningwherein the object is to intensify reflection points on a cathode raytube, a short burst of ultrasonic energy will be transmitted by thepiezoelectric transducer into the body in the form of a narrow beam. Asthis beam progresses into the body it encounters tissue substances andinterfaces between tissue structures which scatter back some of theincident energy. The returning signals or echoes are converted back intoelectrical signals by a receiver transducer which may be the sameelement as the transmitting transducer. The nature of the echoesscattered back in the direction of the receiver transducer is extremelyvaried and depends upon the nature of the tissues responsible for thescattering. A tissue structure which is small compared to the wavelengthof the insonifying energy will scatter energy equally in all directions;i.e., there will be diffuse reflectances. Tissue structure which islarge and flat, however, will function as a mirror and reflect theincident energy in one direction; i.e., specular reflectances willresult. Generally, body tissue will exhibit a combination of diffuse andspecular reflectance patterns. It has long been desired in the art toenhance the diffuse reflectances relative to the specular reflectances.Such enhancement of the diffuse reflectances will produce an improvedimage as the specular echoes tend to be one or two orders of magnitudelarger than the diffuse reflectances. Enhancement of diffusereflectances has not previously been successfully accomplished inultrasonic scanners intended for medical purposes partly because thelarge specular echoes overpower and obliterate the weaker diffusedechoes in both the penetration depth; i.e., range; and azimuthdirections. This obliteration, in part, is a result of the presence ofside lobes in the transmitted signal and thus in the echoes; side lobesbeing inherently present in a diffraction limited energy beam andresulting from fringing effects. Thus, ultrasound directivity patternsnot only have a central main lobe, through which most of the energyreturns, but also include side lobes through which off-axis signals mayenter. If the main lobe is directed towards a weak echo, a strongeroff-axis signal such as a specular echo may enter the side lobes andcompletely obliterate the small signal that is on-axis. It is also to benoted that very large echoes can saturate the amplifiers coupled to thereceiver transducer thereby resulting in the "blooming" of the displayon the cathode ray tube with the resultant obliteration of smallsignals.

In accordance with one embodiment of the present invention the diffusereflectance may be enhanced through the use of a separate receiver inthe form of a segmented annulus. As discussed in the description of FIG.3, the electrode annulus representing the receiver may be divided intoseveral elements by segmenting an outer electrode ring on both sides ofthe transducer into corresponding sections. The electrodes are connectedcyclically; i.e., a "first" rear electrode is connected to a "second"front electrode, the "second" rear electrode is connected to a "third"front electrode, etc. The electrodes are thus electricallyinterconnected in a series aiding configuration. When reflected energyis received equally by all regions of the annulus, characteristic of adiffuse reflectance, voltages which add together are generated. Aspecular echo, if it strikes the annulus at all, will strike only one ortwo regions where segments of the receiver ring are present. Thus, byway of example, if there are ten elements in the receiver, a diffuseecho would generate a voltage ten times higher than an equal magnitudespecular echo impinging on a single segment.

It is to be understood that, rather than connecting all of the elementsin series, each pair of front and rear electrodes may be coupled to aseparate amplifier and the amplified signals processed as desired. Byway of example, the amplified signals from all of the electrodes couldbe averaged to produce a result which would be the same as a seriesaiding configuration. Also, if more complex signal processing isdesired, signals commensurate with all of the echoes being ofapproximately the same magnitude could be accepted for display while thedisplay would be inhibited if there was a wide discrepancy in theamplitude of the signals received at the segments around the annulus.

In accordance with another embodiment, which has achieved exceptionallygood results, all of the electrode rings of either of the transducers ofFIGS. 3 and 4 may be used as both transducing and receiving elements.The use of all electrode rings for focusing in a transducing mode andfor receiving is particularly advantageous when employing the transducerconfiguration of FIG. 4.

Referring now to FIG. 5, the transducer portion of the head 10 of theultrasonic body scanner depicted in FIG. 1 is shown in cross-section.The principal elements of the transducer subassembly are the sonicgenerator and a scanning mirror. The sonic generator includes a focusedpiezoelectric crystal 40 while the mirror has been indicated at 50. Boththe sonic generator and mirror are mounted within a housing 52 which ispreferably molded from an elastomer or other plastic having suitablesound absorption characteristics. The lower end of housing 52, as theapparatus is shown in FIG. 6, will be mated to the bladder 12 which isbrought into contact with the patient. Housing 52 will be filled with asuitable sound transmitting liquid and the front or transmitting face ofcrystal 40 and the face of mirror 50 will be immersed in this liquid.The "tubular" lower portion of housing 52, through which the ultrasonicbeam is transmitted and via which the echoes are received, is providedwith ribs 54 as shown. The purpose of ribs 54 is to dissipate any strayreflections; particularly from side lobes in the signal propagated fromthe crystal 40. The "annulus" 56, which defines the entrance opening tothe cavity in housing 52 in which the scannable mirror 50 is positioned,will also serve to dissipate stray reflections and attenuate anyreflectance from the edge of mirror 50.

Mirror 50, when in its median position, is offset with respect to theaxis of the tubular lower portion or entrance aperture of housing 52 tofurther exclude stray body reflections which may result from distortionsof the bladder 12. The optimum offset; i.e., the angle α between a lineX originating at the point of intersection of the axis Y of the soundtransmitting passage in housing 52 with the surface of mirror 50, andperpendicular to the surface of mirror 50, and the axis of the beam ofultrasound energy generated by crystal 40; has been found to beoptimally 15°. The center of mirror 52 will always be intersected by aline through the center of transducer 40.

The sonic generator includes, in addition to crystal 40, a holder 120into which the crystal is fitted. Holder 120 is filled with a material122 which will absorb energy radiated from the rear surface of thecrystal. Holder 120 also supports the conductors which are connected tothe electrodes on the crystal and suitable isolation, summing andpreamplifier circuitry. An individual "pulse" generator, which will be alow impedance source of electrical energy, will customarily be connecteddirectly to each transducing electrode ring. Considering the transducerof FIG. 4, all of the electrode rings will also be connected to asumming circuit which, in turn, is coupled to a preamplifier.

In the disclosed embodiment mirror 50 comprises a flat surfacedstainless steel disc. The mirror is secured, by means of a suitableadhesive, to a diaphragm 64. The diaphragm 64 is secured as shown so asto function as a seal which renders housing 52 hermetic. The backsurface of mirror 50 is rigidly attached, by any suitable means, to ahemispheric shaped member 66 which functions as a ball joint; theaforementioned line through the center of transducer 40 intersecting thecenter of the ball joint. Ball member 66 cooperates with bearingsurfaces formed on a support table 68; diaphragm 64 being clampedbetween table 68 and housing 52. Ball member 66 is provided with asocket which receives an actuating rod 69. Rod 68 is driven so as tocause the scanning of mirror 50. The movements of actuator rod 68 arecontrolled, in the manner to be described below in the discussion ofFIGS. 6 and 7, by a drive mechanism which is partly shown at 70.

Referring now to FIGS. 6 and 7, the drive for mirror 50 comprises afirst or primary motor 72, which is preferably a stepping motor, and asecond tilt control motor 74, which may also be a stepping motor. Motor72 drives a pulley 86 via a drive system including pulley 76, belts 78and 84 and an idler shaft 80. A pair of idler pulleys are mounted onshaft 80 below a support plate 81 and a flywheel 82 is mounted on shaft80 above plate 81. Pulley 86 is keyed to a rotatable shaft 88 on whichare mounted a pair of conjugate cams 90 and 92. A pair of cams, whichare the direct opposites of one another, are employed in the interest ofavoiding the use of a spring to hold the cam followers against the cams.The use of conjugate cams 90 and 92 thus minimizes the size of drivemotor 72; this being particularly true at high speeds when the followerstend to lift off the cams.

The cam-cam follower relationship may be clearly seen from FIG. 6. Thecam followers 94 and 96 are respectively mounted at first ends of arms98 and 100 and cooperate with respective cams 92 and 90. The second endsof arms 98 and 100 are affixed to a transversely oriented actuator arm102. Arm 102 supports, by means of spaced bearings, a further actuatorarm 103 (shown partially in phantom). Arm 103 follows any transversemovements of arm 102 but is capable of longitudinal movement relative toarm 102. Operation of primary scan motor 72 causes rotation of cams 90and 92 with a rocking motion of actuator arm 102 resulting; the arm 102pivoting about a pivot shaft 104. This oscillatory motion of arm 102 istransmitted to mirror drive shaft 68 by connector 70' formed on the endof arm 103. Thus, operation of primary drive motor 72 results in themirror 50 being scanned back and forth (up and down as the apparatus isshown in FIG. 6) so that each point on the mirror will transcribe a linehaving a slightly arcuate shape. This, in turn, will cause the focalpoint of the ultrasonic beam to transcribe a line located at a depth inthe patient; i.e., a distance from crystal 40; determined either by thenatural focal length of crystal 40 or some other distance as selectedthrough the electronic focusing of the transducer.

In order to shift the scan line to the left or right as the apparatus isdepicted in FIG. 6, the position of a parallel plane cam 106 will bemoved under the control of stepping motor 74; motor 74 driving cam 106via worm gear 108 and gear 110 whereby cam 106 will pivot about shaft112. The end of arm 103 disposed oppositely to connector 70' is providedwith a bearing surface 113 which rides on cam 106 as arm 103 follows thescanning motion of arm 102. Each time cam 106 is repositioned, the scanline will be stepped to a new position by tilting the mirror 50 in adirection generally transverse to the scan line as determined by themotion of arm 102 resulting from rotation of cams 90 and 92.

Referring again to FIG. 7, slotted disc 114 is mounted on and rotateswith shaft 88. A photoelectric sensor, indicated generally at 116 andincluding a light source and light responsive detector element, ismounted so as to sense the passage of the slot or slots in disc 114. Thesignals generated by detector 116 are used to synchronize the display tothe position of mirror 50.

Referring now to FIG. 8, a circuit block diagram of a control system fora preferred embodiment of the present invention is shown. The controlsystem of FIG. 8 is intended for operation with a transducer of the typedepicted in FIG. 4 wherein the front surface of the crystal iscompletely covered with electrically conductive material and the rearsurface of the crystal has electrodes disposed thereon in the form of aplurality of concentric rings; the control of FIG. 8 specifically beingapplicable to a transducer with eleven such electrode rings. A highlyschematic cross-sectional view of the electrode appears in FIG. 9 whileFIG. 10 is a wave form diagram showing voltages which appear at variouspoints within the control circuit of FIG. 8.

Continuing to refer to FIG. 8, the control system includes circuitry for"firing" the electrode rings on the transducer crystal in the propersequence so as to achieve the desired depth of focus of the transmittedultrasonic "beam". The control circuitry of the disclosed embodiment hasthe capability of selecting six zones or depths of focus with focallength Z3 being the natural focus of the shaped transducer crystal. Whenall eleven electrode rings are simultaneously energized, the resultingbeam of ultrasonic energy will be focused at the natural focal length Z3of the transducer. The control circuitry of the preferred embodiment ofthe invention also includes means for selecting different modes ofoperation, means for controlling the scanning of the ultrasonic beam asdescribed above and means for processing and displaying and/or recordingreceived echoes.

The various subsystems of the control circuitry of FIG. 8 are responsiveto the outputs of a data acquisition and display timing generator 200(FIG. 8B). Timing generator 200 receives, as input signals, the outputof a clock pulse generator 202 and a output from a mode control selectorcircuit 204. Timing generator 200 divides down the output of clock 202to provide, in the proper sequence, timing pulses which control theoperation of ramp voltage generators 210 (FIG. 8A), 244 (FIG. 8C) and272 (FIG. 8D) and controls the sampling rate of an analog-to-digitalconverter 258 (FIG. 8C). Timing generator 200 also produces gatingsignals, corresponding to the six possible depths or zones of focus, fordelivery to a zone select circuit 206. These gating signals are in theform of six sequential control pulses have the same width.

The mode control circuit 204 may comprise a "memory" including aflip-flop circuit which will be set depending upon the mode of operationselected by the operator. The "EXPLORE/QUALITY" selector enables theoperator to vary the mode of scanning between a real time or "EXPLORE"mode, wherein the beam is scanned at a first and relatively fast rate,and a "QUALITY" mode wherein the ultrasonic beam is scanned at a secondslower rate. Thus, after determining an area of interest in real time, aquality scan along the same plane may be initiated. The "HOLD/UNHOLD"control, which will not be further described herein, when energizedstops additional information from being loaded into the storage deviceswhich comprise the receiver-display portion of the system. The "TAKE"control, when energized, controls the operation of a camera 34 wherebyphotographs may be taken to provide a permanent record of the patientthroughput. The "SECTIONS" control comprises an enabling switch whichprovides a gating signal for the control for motor 74 which produces themultiple scan mode of operation. The switches which generate the inputsignals to mode control 204 are located on the control panel 18.

Presuming that the "EXPLORE" mode has been selected by the operator, andthe control system has been initialized in the manner known in the art,timing generator 200 will provide sequential gating signals to the zoneselect circuit 206 as described above. Zone selector circuit 206 alsoreceives, as a second input, a signal generated by operation of one of aplurality of push button type controls which are also located on controlpanel 18; there being a separate push button for each of the sixpossible beam focal lengths. The zone select circuit 206 includes acounter, gates and latches which provide, in response to the two inputs,a digitally coded output signal which is commensurate with the zoneselector button which has been operated. This digitally coded zonesignal is applied as the control input to a zone control circuit 208(FIG. 8A). Zone control circuit 208 may comprise a digital-to-analogfunction generator which provides a steady state output voltage having amagnitude commensurate with the selected zone.

The output voltage from zone control circuit 208 is provided as thecontrol input to ramp voltage generator 210; ramp voltage generator 210receiving a gating signal which functions as a "start ramp" command fromtiming generator 200 as previously described. Ramp voltage generator 210may comprise a conventional controllable sweep voltage generator whichproduces a sawtooth voltage wave form having a slope which varies inaccordance with the level of the control input; i.e., the slope of theoutput voltage of ramp voltage generator 210 is determined by the inputto the ramp voltage generator from the zone control circuit 208.Referring to FIG. 10A, three separate ramp voltage generator outputsrespectively commensurate with zones or beam focal lengths Z1, Z3 and Z6are depicted.

The sweep voltage outputed from ramp voltage generator 210 is deliveredas the input to a plurality of identical voltage comparator circuits212; the number of comparators being commensurate with the number ofelectrode rings on the transducer. Each of voltage comparators212-212^(n) is connected to receive a respective input bias voltageVl-Vn. The bias voltages are compared with the instantaneous magnitudeof the ramp voltage from generator 210 in comparators 212. The biasvoltage or comparator levels are also represented on FIG. 10A. When theramp generator output equals the comparator bias level, the comparatorswill individually deliver gating signals to an associated one shot delaymultivibrator 214. As indicated in FIG. 10B, the delay multivibratorshave preselected periods. The time of gating of multivibrators 214 will,as should be obvious from the discussion above, be a function of theslope of the ramp voltage provided by generator 210.

Each of delay multivibrators 214 is connected to a separate wave formgenerator; one of these wave form generators being indicated generallyat 216 and all eleven generators 216 in the embodiment being disclosedbeing identical. The purpose of the wave form generators 216 is toprovide a burst of electrical energy at a preselected frequency, forexample 2.5 MHz, and to modulate this burst of energy by a Gaussianenvelope. The wave form generators 216 each include a square waveoscillator 217 which is gated into operation in response to the trailingedge of the output pulse provided by the delay multivibrator 214 towhich the wave form generator is connected. Oscillator 217 provides asquare wave output signal which is delivered as the input to an up-downcounter 218. Counter 218, in turn, provides an input signal to a decoder220. Decoder 220, which may for example comprise a Texas InstrumentsType 7442 decoder, has four inputs connected to counter 218 and, in theexample shown, six outputs which are connected, via a resistor networkcomprising resistors R1-R6, to the inputs to a pair of summingamplifiers 224 and 226. The summing amplifiers sum the current throughthe plurality of resistors to which the amplifier input is connected andprovide an output signal commensurate therewith. The output signals fromsumming amplifiers 224 and 226 are provided as the inputs to adifferential amplifier 228. The wave form generator 216 also includes adivide-by-two circuit 222 which provides a signal from decoder 220 backto counter 218 to control the direction of counting. FIG. 10C shows thewave form of the signal which appears at the output of differentialamplifier 228. It may be seen that this signal has a Gaussian envelope;i.e., the output of differential amplifier 228 increases gradually toits maximum value and then decreases gradually. The shape of theenvelope will be a function of the size of resistors R1-R6 and theirmanner of interconnection between decoder 220 and summing amplifiers 224and 226.

It is to be observed that oscillator 217 may be variable in frequency asshown. Thus, the present invention encompasses the ability to change thefrequency of drive of the transducer to select the optimum to achievethe best resolution or maximum depth of penetration of the beam. Use ofa variable frequency transducer is permitted by the employment of a lowQ crystal in combination with a highly damped system.

The output of the wave form generators 216, there being eleven suchoutputs in the embodiment being described, are delivered to individualdriver amplifiers. The drivers are indicated in FIG. 8A generally at 230and will comprise linear amplifiers with adjustable feedback resistorswhereby the gain of the drivers is individually adjustable. The outputsof the drivers 230 are individually connected to the appropriateelectrode rings on the transducer; the transducer being indicated onFIG. 8A at 232. From joint consideration of FIGS. 8-10, it may be seenthat the selection of a particular zone through operator depression of acontrol button associated with zone select circuit 206, the buttonsbeing located on panel 18, will vary the times of relative firing of theelectrode rings on transducer 232 to thereby vary the depth of focus ofthe beam of ultrasonic energy. Side lobe suppression is enhanced by"shading" the electrodes through adjustment of the gain of the drivers;i.e., side lobes are minimized by apodization wherein differentmagnitude drive voltages are applied to the electrode rings.

Referring again to FIG. 8B, a further output of timing generator 200 isdelivered as the control input to a stepper motor control circuit 234which provides the control signals for stepping motor 72 (FIG. 6). Thestepper motor control 224 may comprise a commercially available circuitwhich, in response to control signals received from timing generator200, causes the rotor of stepping motor 72 to move through apredetermined angle. When in the EXPLORE mode, motor 72 will be advancedby one step for each sweep of ramp voltage generator 210. In the"QUALITY" mode, as a result of the control exercised over the output oftiming generator 200 by mode control 204, motor 72 will be stepped withevery sixth firing of transducer 232. As described above in thediscussion of FIG. 7, the output shaft of stepping motor 72 is coupledto an index signal generator comprising disc 114 and sensor package 116.The output of the index signal generator is fed back as a synchronizingsignal to a stepping counter 240. The motor control pulses from steppercontrol 234 are delivered as input signals to counter 240. Counter 240,since the number of counts required to make a complete sector scan areknown, is able to provide information commensurate with the angle ofdeflection θ of mirror 50 and thus with the aiming of the beam ofultrasonic energy and particularly whether the beam is in the left orright half of the sector being scanned. Because of the type of drive, asdiscussed above in the description of FIGS. 5 and 6, it is not necessarythat stepping motor 72 be reversed to accomplish the desired scanning ofmirror 50 prior to initiating firing of transducer 232.

If multiple plane scanning is desired, the operator will operate the"SECTIONS" control on panel 18 thereby causing the mode control 204 toprovide an enabling signal to the stepper motor control 242 for motor74. Motor control 242 also receives, as an input, an "end of sector"signal from the stepping counter 240 associated with motor 72. Furtherinputs to stepper motor control 242 are a signal from a stepping counter246 and signals generated by thumb wheel switches, located on controlpanel 18, which permit the operator to manually control the spacingbetween the multiple planes or sectors and the number of planes desired.Stepper control 242, in response to the enabling signal from modecontrol 204 and the initiate or "end of sector" signal from steppingcounter 240, will command stepping motor 74 to advance in steps having amagnitude determined by the thumb wheel switches control input. In thesame manner as with stepping motor 72, the index generator 114-116provides a synchronizing signal which may be fed back to counter 246;counter 246 also receiving the motor control pulses from stepper control242. Counter 246 provides a signal to control 242 indicative of theposition of its rotor, and thus indicative of the angular φ of mirror50, which is compared in control 242 with the desired final position asestablished by the thumb wheel switch inputs.

Turning now to FIGS. 8C and 8D, all of the electrode rings on transducer232 are connected to the input of a preamplifier 250 for initial signalenhancement. The output of preamplifier 250 is delivered as the input toa variable gain amplifier 252. Variable gain amplifier 252 is providedwith a video gain control adjustment which may merely be in the form ofa potentiometer. Amplifier 252 also receives a time gain control inputsignal from ramp voltage generator 244. Ramp voltage generator 244comprises a controllable sweep voltage generator. The slope or slopes ofthe output voltage of generator 244 is selected by the operator by meansof adjustment of a plurality of potentiometer inputs. Ramp voltagegenerator 244 receives a "start" signal from the timing generator 200,as described above, and provides an output signal which varies the gainof amplifier 252 in part as a function of the time which has elapsedsince the most recent firing of the transducer 232. The "start" signalfor generator 244 is delayed subsequent to the "start" of ramp voltagegenerator 210 (FIG. 8A) by an amount corresponding to the time requiredfor the ultrasonic energy produced by transducer 232 to reach thepatient's skin line. By adjustment of the inputs to ramp voltagegenerator 244, the operator may vary gain of amplifier 252 such that theamplitude of signals commensurate with received echoes passed byamplifier 252 will be a function of the distance the ultrasonic energyhas traveled; i.e., those signals which have traveled the greaterdistance, and have thus been subject to greater attenuation, will beenhanced in comparison with echoes returning from lesser depths. Theoutput of ramp voltage generator 244 may have as many as four differentslopes in the interest of achieving the echo related signal enhancementwhich provides the most informative display.

The output from amplifier 252 is applied to a detector 256. Detector256, in turn, provides an input voltage level, which varies as afunction of the strength of the received echoes taking into account thegain compensation provided by amplifier 252, to an analog-to-digitalconverter 258. Converter 258, under the control of timing signals fromtiming generator 200, samples the output of detector 256 at preselectedintervals which may, for example, be every one microsecond. Each timethe analog-to-digital converter 258 is sampled, a digitally coded signalcommensurate with the instantaneous input voltage to converter 258 isdelivered to a line buffer 260.

Buffer 260 comprises 4×256 bits of temporary storage. Buffer 260functions to gather the received data which is thereafter, under thecontrol of a load and unload control circuit 260, transferred into adynamic memory 264 which may, for example, comprise a serial shiftregister. The load and unload control 262 also controls outputing ofdata from storage circuit 264 to a grey scale code converter 266. Thecontrol inputs to the load and unload control, which may comprise merelya plurality of gating circuits, are derived from stepping counter 240and zone control circuit 206. The input to load and unload controlcircuit 262 derived from counter 240 determines the address in buffer260 where the sampled data is stored. The input to load and unloadcontrol 262 provided by the zone select circuit 206 controls the loadingand unloading of buffer 260 and memory 264. Stored data is transferredfrom buffer 260 into memory 264 subsequent to receipt of all echoesassociated with a single "firing" of transducer 232 in the "EXPLORE"mode and after every sixth burst in the "QUALITY" mode.

Since photographic film is nonlinear, and it is desirable to produceequal steps in shading for the various echo levels received, the greyscale code converter 266 is utilized. Converter 266 generates a transferfunction whereby the information outputed from storage circuit 264,which is in the form of four bits, will be converted into six bits ofinformation commensurate with sixty-four discrete levels of grey. Thedigital output information from converter 266 is applied to adigital-to-analog converter 268. The output of converter 268 functionsas the modulation input signal to an oscilloscope 270 located withinequipment cabinet 30.

Referring to FIG. 8D, the circuitry for synchronizing the display withthe scanning of the ultrasonic beam is shown. The display controlcircuitry includes ramp voltage generator 272 which receives the "startramp" control pulses from timing generator 200. The sweep voltageproduced by generator 272 is applied as first inputs to a pair of analogmultipliers 274 and 276. The display control circuitry also includes aprogrammed read only memory 278 which receives signals provided by thecounter 240 which is associated with the sector scan drive motor 72. Inresponse to the output signal provided by counter 240, which isindicative of the angular relationship of the mirror to its centeredposition, memory 278 will output a pair of digital signals respectivelycommensurate with the sine and cosine of the instantaneous mirror angleθ. These sine and cosine signals are converted, in respecteddigital-to-analog converters 280 and 282, to analog signals and appliedas second inputs to respective multipliers 274 and 276. Accordingly,multiplier 274 will provide an output signal having a magnitude whichvaries as a product of the sine of the angle θ of mirror 50 relative toits undeflected position and the time which has elapsed since thebeginning of the scan. Similarly, multiplier 276 will also provide anoutput signal corresponding to the product of the mirror angle θ and theelapsed time. The output of multiplier 276 is applied to an amplifier284 and the output of this amplifier controls the "X" deflection ofoscilloscope 270. The output of multiplier 274 is, depending on thestatus of a switch driver circuit 286, applied either to a "right half"amplifier 288 or a "left half" amplifier 290. Switch driver 286 iscontrolled by the output of counter 240 and insures that the appropriateamplifier output will be utilized to obtain the requisite "Y" deflectionsignal for oscilloscope 270 as a function of the position of mirror 50.FIG. 8D indicates the display nomenclature and shows why it is necessaryto employ a switch driver circuit 286 and amplifiers 288 and 290 inorder to form, on the CRT of oscilloscope 270, an accuraterepresentation of the scanning plane. The output signal from either ofamplifiers 288 or 290 is applied as the "Y" axis deflection controlsignal for oscilloscope 270.

Referring again to FIG. 8C, a TV camera 292 is located within equipmentcabinet 30 and, via a splitter plate 294, observes the image formed onthe CRT of oscilloscope 270. The output of camera 292 is delivered to TVmonitor 26 (FIG. 1).

The still camera 34 also views, via splitter plate 294, the display onoscilloscope 270. By depressing the "take" button associated with modecontrol circuit 204, the operator can cause the shutter of the camera 34to be tripped whereby a photograph may be taken whenever the operatorobserves something of interest on the TV monitor thus preserving apermanent record for further study. The apparatus will also include anautomatic film advance which is energized when the camera shutter isoperated.

While preferred embodiments have been shown and described, variousmodifications and substitutions may be made thereto without departingfrom the spirit and scope of the invention.

Accordingly, it is to be understood that the present invention has beendescribed by way of illustration and not limitation.

What is claimed is:
 1. Apparatus for generating a scanning energy beamfor non-destructive and non-invasive testing comprising:transducermeans, said transducer means being responsive to electrical drivesignals for generating ultrasonic energy, the thus generated ultrasonicenergy being radiated in the form of a beam having an axis; reflectormeans positioned in the path of the beam of ultrasonic energy radiatedfrom said transducer means whereby said energy will impinge upon a firstsurface of said reflector means thereby changing the direction of travelof the ultrasonic energy, an axis through the center of said reflectormeans intersecting the axis of said beam of ultrasonic energy; driveshaft means engaging a second side of said reflector means disposedoppositely to said first surface thereof; arm means, said arm meansbeing coupled at a first end to said drive shaft means and beingvariable in length; means pivotally supporting said arm means adjacentthe second end thereof, said supporting means permitting longitudinalmovement of at least a portion of said arm means to vary the effectivelength thereof; first motor means; first cam means connected to said armmeans and driven by said first motor means, said first cam meansimparting a pivoting motion to said arm means; second motor means; andsecond cam means driven by said second motor means, said second cammeans cooperating with said arm means to vary the longitudinal positionof the first end thereof whereby said drive shaft means will move in afirst direction in response to motion of said first cam means and willmove in a second direction generally transverse to said first directionin response to movements of said second cam means.
 2. The apparatus ofclaim 1 wherein said drive shaft means comprises:bearing means affixedto a second side of said reflector means disposed oppositely to saidfirst side thereof, said bearing means including a bearing surface inthe form of a portion of a sphere; housing means difining a surfacewhich has a complementary shape to and cooperates with said bearingsurface; and a drive shaft engaging said bearing means at a first endand passing through an aperture in said housing means, said drive shaftbeing engaged by said arm means.
 3. The apparatus of claim 2 whereinsaid reflector means comprises:a flat plate mirror, said axis throughthe center of said reflector means mirror being transverse to thesurface thereof.
 4. The apparatus of claim 3 wherein said axes intersectat the center of the sphere defined by said bearing surface and whereinsaid reflector means rotates about said intersection.
 5. The apparatusof claim 4 wherein said first cam means comprises:a pair of conjugatecams, said pair of cams being driven by said first motor means; and apair of cam follower means respectively associated with the cams of saidconjugate pair, said cam follower means being connected to said armmeans.
 6. The apparatus of claim 5 wherein said housing means furthercomprises:an exit opening, said exit opening having a longitudinal axis;means supporting said transducer means; and means supporting saidreflector means mirror for angular movement relative to the axis of thepath of the energy generated by said transducer means.
 7. The apparatusof claim 6 wherein said reflector means supporting means includes:aflexible member attached to said reflector means, said flexible memberfunctioning as a seal to prevent leakage of fluid from within saidhousing means.
 8. The apparatus of claim 7 wherein said first motormeans comprises:a stepping motor; means for generating control pulsesfor energization of said first stepping motor; and means for couplingthe motion of the output shaft of said first stepping motor to saidfirst cam means.
 9. The apparatus of claim 8 wherein said housing meansexit opening axis is angularly related to and intersects said axisthrough the center of said reflector means mirror and transverse to thesurface of said mirror when said mirror is in an undeflected position.10. The apparatus of claim 5 wherein said first motor means comprises:astepping motor; means for generating control pulses for energization ofsaid first stepping motor; and means for coupling the motion of theoutput shaft of said first stepping motor to said first cam means. 11.Apparatus for generating a scanning energy beam for non-destructive andnon-invasive testing comprising:transducer means, said transducer meansgenerating ultrasonic energy in response to electrical stimulation, theultrasonic energy being radiated from said transducer means in the formof a beam having an axis, said transducer means being steerable to causethe beam of ultrasonic energy to scan in accordance with a desiredpattern; drive shaft means, said drive shaft means engaging saidtransducer means; first motor means, said first motor means including amotor having a rotatable output shaft; and first cam means coupling saidfirst motor means motor output shaft to said drive shaft means at apoint displaced from the point of engagement of said drive shaft meanswith said transducer means, said first cam means including:a pair ofconjugate cams, said pair of cams being driven by said first motormeans; a pair of cam follower means respectively associated with thecams of said conjugate pair; and arm means supporting said cam followermeans, said arm means having a first and a second end and being mountedadjacent the first end thereof for motion about a pivot point inresponse to the motion of said cams, the second end of said arm meansbeing connected to said drive shaft means whereby rotation of said firstmotor means motor output shaft will produce scanning of the beam ofultrasonic energy.
 12. The apparatus of claim 11 wherein said transducermeans includes a stationary ultrasound generator and reflector meansmovable relative thereto, said reflector means being connected to saiddrive shaft means.
 13. The apparatus of claim 12 wherein said ultrasoundgenerator comprises a single piezoelectric crystal.
 14. The apparatus ofclaim 11 wherein said transducer means comprises a single piezoelectriccrystal.
 15. Apparatus for generating a scanning beam fornon-destructive and non-invasive testing comprising:stationarytransducer means, said transducer means being responsive to electricaldrive signals for generating ultrasonic energy, the thus generatedultrasonic energy being radiated from a first face of said transducermeans in the form of a beam having a symmetry axis which extendsoutwardly from said first face; reflector means positioned in the pathof the beam of ultrasonic energy radiated from said stationarytransducer means whereby said energy will impinge upon a first surfaceof said reflector means thereby changing the direction of travel of theultrasonic energy, said reflector first surface having a center, an axisextending through the center of said reflector means and perpendicularto said first surface intersecting the axis of said beam of ultrasonicenergy at an angle; bearing means affixed to said reflector means secondsurface, said bearing means including a hemispherical bearing surface,the axis of the beam and the axis through the center of said reflectormeans intersecting at the center of the sphere defined by saidhemispherical bearing surface; housing means defining a complimentarybearing surface which cooperates with said bearing means hemisphericalbearing surface; a first drive shaft engaging said bearing means; firstmotor means, said first motor means including a motor having a rotatableoutput shaft; and first cam means connected to said first drive shaftand driven by said first motor means, said first cam means imparting apivoting motion to said first drive shaft to cause said reflector meansto rotate about said intersection of said axes.
 16. The apparatus ofclaim 15 wherein said first cam means comprises:a pair of conjugatecams, said pair of cams being driven by said first motor means; a pairof cam follower means respectively associated with the cams of saidconjugate pair; and arm means supporting said cam follower means, saidarm means having first and second ends and being mounted adjacent thefirst end thereof for motion about a pivot point in response to themotion of said cams, the second end of said arm means being connected tosaid first drive shaft.
 17. The apparatus of claim 16 furthercomprising:housing means supporting said transducer means, said housingmeans having an exit opening for the ultrasonic energy and defining aliquid flow path between said transducer and said exit opening; andmeans supporting said reflector means within said housing, saidreflector means being at least partly immersed in the liquid whichdefines the said flow path, said supporting means permitting movement ofsaid reflector means.
 18. The apparatus of claim 17 wherein saidreflector means supporting means includes:a flexible member attached tosaid reflector means, said flexible member functioning as a seal toprevent leakage of fluid from within said housing means.
 19. Theapparatus of claim 17 wherein said housing means exit opening has anaxis and wherein said exit opening axis is angularly related to an axistransverse to the surface of said reflector means in its undeflectedposition.
 20. The apparatus of claim 1 wherein said first motor meanscomprises:a stepping motor; means for generating control pulses forenergization of said first stepping motor; and means for coupling themotion of the output shaft of said first stepping motor to said firstcam means.
 21. The apparatus of claim 15 wherein the motion imparted tosaid first drive shaft by said first cam means causes the beam ofultrasound energy to scan linearly and wherein said apparatus furthercomprises:means for causing said first drive shaft to move in adirection generally transverse to the direction of motion impartedthereto by said first cam means whereby the linear scan of the beam maybe caused to transcribe a plurality of generally parallel paths.
 22. Theapparatus of claim 21 wherein said stationary transducer means includesa single piezoelectric crystal.
 23. The apparatus of claim 21 whereinsaid reflector means first surface is planar.
 24. The apparatus of claim15 wherein said stationary transducer means includes a singlepiezoelectric crystal.
 25. The apparatus of claim 15 wherein saidreflector means first surface is planar.